Identify the problem, then formulate and solve the problem. Scenario: You are an
ID: 2080354 • Letter: I
Question
Identify the problem, then formulate and solve the problem. Scenario: You are an engineer at a large manufacturing plant. The manager calls a meeting with the engineering team, and he is concerned about the plant's monthly electric bill, which has been very high for two months in a row. After investigating, you discover that the existing Utility Rate Schedule for Large Industrial customers has a penalty clause, which is triggered when the overall plant power factor drops below 0.96. Checking the monthly electric bills and the plant metering information, you obtain the following information relative to the past two months electrical usage: June July Peak 12.6 MW Peak 12.8 MW pf 0.94 lagging pf 0.93 lagging The line voltage in the plant is 480 V.Explanation / Answer
Here the problem is a penalty on power factor decrease below 0.96.
To maintain power factor above or equal to 0.96 is to install a capacitor which can compensate reactive power of the manufacturing plant.
Considering the month of July and compensate the reactive power consumed in that month because power factor is less in that month compared to June.
Reactive Power consumed when power factor if maintained at 0.96 is
Q = P*tan(phi) ; where phi = cos-1(0.96) = 16.260
Q = 12.8*106*tan(16.26) = 3733283.711 = 3.733 MVar
Actual reactive power consumed is
Qact = P*tan(Phiact) ; where Phiact is cos-1(0.93) = 21.560
Qact = 12.8*106 * tan(21.560) = 5058883.702 Var = 5.058 MVar
The capacitor bank need to be installed should compensate reactive power of
Qc = Qact - Q = 5.058 - 3.733 = 1.325 MVar